1. Field of the Invention
The present invention relates to wireless tag readers and writers having a read/write box in which documents with wireless tags is stored and in which information is read and written from/to the wireless tags.
2. Description of the Related Art
At delivery control and processing of mail including documents and envelopes, a large amount of mail can be processed at a time in such a manner that wireless tags are stuck to the mail, to which data including positional information on the channel of distribution is written, and the data is read through a read antenna. This technique is disclosed in, for example, Japanese Publication No. 11-175621.
To write or read data to/from wireless tags, wireless tag readers and writers having a read and write box for the objects to be controlled or processed having the wireless tags are used. The wireless tag reader and writer has a read antenna for reading the position of the wireless tags on the top of the read and write box, and starts writing with a write antenna when the wireless tags enter a normal writing area.
FIG. 1 is a side sectional view showing the schematic structure of the conventional wireless tag reader and writer. In the wireless tag reader and writer, specified pieces of mail 3 with wireless tags 2 are stacked in a read and write box 4 through an opening 1. The wireless tags 2 of the mail 3 stored are recognized by a read antenna 8 disposed on the top of the read and write box 4, wherein when the mail 3 is determined to be in a normal write area, data is written to the wireless tags 2 through a write antenna 5 disposed inside the read and write box 4.
In the conventional wireless tag reader and writers, when a specified amount of mail 3 heaps in the read and write box 4 for the mail 3 with the wireless tags 2 through the opening 1, the mail 3 is displaced toward the opening 1 because of the thickness of the wireless tags 2. The wireless tags 2 of several pieces of mail 3 therefore get out of the normal write area 6 of the write antenna 5, as shown in FIG. 1. This caused the problem that the wireless tags 2 outside the write area, as indicated by a triangle 7, are also recognized by the read antenna 8, to which data is written through the write antenna 5.
Even if the mail 3 does not get out of position, the foregoing problem has occurred because of the way operators put the mail 3, i.e., in the case where operators do not put the wireless tags 2 deep enough into the read and write box 4.
Furthermore, also when radio waves radiated from the read antenna are diffused or reflected by the other walls, the wireless tags outside the normal write area are received by the read antenna, posing the problem of hindering accurate position finding. Such events prevent normal writing to the wireless tags, taking the trouble of rewriting, or in the worst case, posing the problem that the subsequent processing is performed without writing.